This invention relates to the mono-chlorination or monobromination of a C.sub.9 -C.sub.18 n-paraffin to produce an alkylating agent. In one aspect, this invention relates to a process for producing an alkyl-aromatic by monohalogenating a C.sub.9 -C.sub.18 n-paraffin and alkylating an aromatic with the monohalogenated n-paraffin to provide an alkylaromatic intermediate in detergent alkylate production. More specifically, this invention relates to the removal of oxygen-containing hydrocarbonaceous compounds formed by the oxidation of a C.sub.9 -C.sub.18 n-paraffin, which oxygen-containing compounds, when present in admixture with the n-paraffin, inhibit the rate of halogenation of the paraffin. This invention further relates to an improved process for producing an alkylaromatic product from a C.sub.9 -C.sub.18 normal paraffin and a monocyclic aromatic.
Processes for the production of straight chain alkylaromatics have gained considerable importance in the past few years as a result of the demand for control of water pollution. The relevant alkylaromatics are those having an aromatic nucleus bonded at various positions on a linear alkyl chain to a C.sub.9 -C.sub.18 linear alkyl group. When such alkylaromatics are converted to detergents through sulfonation, neutralization, etc., the resulting detergent is more bio-degradable than a detergent of the same chemical composition in which the alkyl chain is highly branched, e.g., detergents prepared from propylene tetramer.
A preferred method for preparing the bio-degradable detergents includes mono-chlorinating or mono-brominating a C.sub.9 -C.sub.18 n-paraffin to form the corresponding mono-halogenated paraffin. The mono-halogenated paraffin is employed as an alkylating agent and is reacted with a monocyclic aromatic, typically benzene, to form the desired biodegradable detergent alkylate precursor.
In mono-halogenating paraffins for use in preparing alkylaromatics, thermal halogenation is preferred over halogenation processes utilizing a catalytic agent. Halogenation processes in which a catalyst is employed typically produce di- or polyhalogenated paraffins in excessive quantities and also produce olefins, which are highly undesirable in a mono-halogenation operation. Thermal halogenation has been found to provide a more selective and easily controllable method of halogenation, giving a higher yield of the desired mono-halogenated paraffins, while producing fewer undesirable side products. Thermal halogenation is also generally preferred because the thermal route obviates the difficulties and expense inherent in handling a catalyst. For example, the presence of water, aromatics and other contaminants is known to have a deleterious effect on halogenation catalysts, and therefore halogenation processes using such catalysts must make provisions for removal of such contaminants. This leads to further complication and expense.
One of the continuing goals in the halogenation art is to increase the rate of halogenation while maintaining the selectivity of the process for producing mono-halogenated paraffins, in contrast to di- and polyhalogenated paraffins or olefins. This is particularly true where the halogen employed is bromine. Bromine is known to react slowly with n-paraffins as compared to chlorine, for example. In many cases, however, bromine is preferred over chlorine as a halogenation agent, since the hydrogen bromide formed in the halogenation reaction is more easily converted to molecular bromine than is hydrogen chlorine converted to molecular chlorine. Since molecular bromine and chlorine are the halogenation agents normally used in such a halogenation process, it is preferred to use bromine rather than chlorine so that recycle of the halogen is facilitated. Prior art recognition that n-paraffins are relatively difficult to halogenate has led to the use of halogenation processes to selectively halogenate and separate isoparaffins from n-paraffins.
I have made the surprising discovery that when the paraffin employed in thermal halogenation contains oxygen-substituted hydrocarbonaceous compounds, such as those formed by air oxidation of a normal paraffin, the oxygen-containing compounds act as inhibitors in the halogenation reaction, even when present in small amounts. The resulting slower rate of reaction necessitates the use of a larger reactor, longer reaction time, etc., and thereby results in undesirable additions to the expense and complication of the operation of a halogenation process.